Process for preparing stable alternating twist yarn



Jan. 7, 1964 A. L. BREEN ETAL 3,116,583

PROCESS FOR PREPARING swam ALTERNATING TWIST YARN 2 Sheets-Sheet 1 FIG. 3

Original Filed Aug. 12, 1958 FIGI m An M j .H 6/ m FI' Wu L .m v ug 7 7 w fl l m i u m n GHQ 0 m m F E m I u I n 4m 6 m F INVENTORS ALVIN L. BREEN MARTIN V. SUSSMAN ATTORNEY 2 Sheets-Sheet 2 ,::Z:::: m M w ZZZ/Z: Z, I, ZZZ/Z: m o

J I d I i I, E n %i% T A III I I III Ls \IIIIIII III II:

\IIIIIII \IIIIIII m A I km; @E

:iiiii: 0

iii/11:: ,IZ/ZTZZZ sis-32:21 5: 5.: Y

II; I i i I \IIIIIII ii: i \II \IIIIIII Jan. 7, 1964 A. BREEN ETAL PROCESS FOR PREPARING STABLE ALTERNATING TWIST YARN Original Filed Aug. 12, 1958 United States Patent Ofi ice 3,116,588 Patented Jan. 7, 1964 8 Claims. (Cl. 57-157) This invention relates to yarn production and handling, and is particularly concerned with twisting as-spun or zero-twist yarn in a continuous manner. More specifically, this invention relates to a novel and useful process and apparatus for continuously twisting such yarn, and to alternating-twist products produced thereby.

This application is a continuation-impart of application Serial No. 598,135, filed July 16, 1956, now US. Patent No. 3,009,309, and a division of application Serial No. 754,912, filed August 12, 1958, now abandoned.

Twisting plays an important part in most textile operations. The need for true twist is indicated by production and end-use considerations. True twist may be needed at relatively low levels, say about 1 turn per inch (t.p.i.), to improve yarn handling characteristics, at the intermediate levels of about 6 to 12 t.p.i. in the case of yarn to be used in textile or industrial applications respectively, and at higher levels, e.g., 30 or more t.p.i. to produce stretch yarns and the like. Such twist accomplishes several purposes, the more important being to improve the runability and quality of the yarn, to compact the yarn bundle, to control fabric appearance and hand, to increase yarn elasticity, and so on. As an alternative to twisting, the use of untwisted or zero-twist yarn in most cases is decidedly unattractive, due mainly to the poor performance of such yarn in many of the common textile operations, such as winding, weaving, and knitting.

Although the need for twisting remains unchallenged, it is a very expensive operation. Twisting requires elaborate and expensive equipment which is both costly and diflicult to maintain, and is a low-output time-consuming operation, being neither a continuous nor a multi-end process. It is estimated that using a conventional uptwister operating at a normal speed of 10,000 rpm, about 11 days are required to produce a single pound of 30 t.p.i. 30- denier nylon yarn. Such low output not only increases the product cost, but creates a definite bottleneck in the otherwise rapid and continuous production of yarn. Moreover, the mechanics of true twisting and additional handling required often results in low yarn quality.

It is apparent that many improvements in the continuous production of yarn would arise from a suitable method and apparatus for continuous, high-speed, inprocess true twisting, but the closest approximation to such twisting resides in conventional false-twisting as employed in the production of the so-called Helanca stretch yarn. False-twisting apparatus is exemplified in US. 2,089,198-199 to Finlayson et al.; US. 2,189,239 to Whitehead; US. 2,111,211 to Finlayson et al.; US. 2,463,620 to Heberlein; and US. 2,741,893 to Vandamme et al. Additional mechanical and pneumatic false-twisters are shown in U.S. 2,100,588 to Claus; US. 2,173,789 to Nickles; US. 2,475,922 to Stockley; US. 2,515,299 to Foster et al; US. 2,526,775 to Slayter et al.; and US. 2,751,741 to Burleson.

All known false-twisters operate in essentially the same manner. In the well-known process for producing socalled Helanca or stretch yarns, a twisted yarn segment is subjected to heat-setting conditions and then backtwisted. False-twisting in the absence of setting has produced only zero-twist yarn, since the twist has been temporary and is automatically removed as the twisted yarn passes through the twisting means. Accordingl, even though false-twisting permits the temporary accumulation of twist in a running yarn line, such twist is of an extremely transitory nature, and the product of such a process is zerotwist yarn. False-twisting alone, therefore, is not a solution to the problems indicated hereinabove. (Truslow, Handbook of Twisting, p. 4041 (1957), Clark Publishing Co., Charlotte, NC).

It is an object of this invention to provide a process whereby yarn is twisted into a stable configuration in a rapid and continuous manner. Another object of this invention is to provide a yarn-twisting process and apparatus whereby freshly formed yarn is continuously twisted prior to initial packaging. A still further object is a yarn twisting process and apparatus whereby yarn is continu ously twisted to produce a stable alternating-twist yarn. Still another object of this invention is to provide a yarntwisting process and apparatus whereby staple fiber roving is twisted to produce a sheaf yarn having a novel structure and characteristics.

A further object of this invention is to produce a stable alternating-twist yarn in which both the yarn bundle and individual filaments within the yarn are twisted. Yet another object is a stable alternating-twist yarn characterized by having successive segments of twist of the opposite direction, the segments not necessarily of equal length, with the net sum of all bundle twist being substantially zero. Yet another object is stable alternatingtwist yarn containing an average of greater than about 1 absolute (disregarding direction) turn of twist per inch. These and other objects, together with means for accomplishing them will appear hereinafter.

According to this invention, a stable alternating-twist yarn is produced by subjecting successive segments of a multifilarnent yarn to the twisting action of a jet of fluid by feeding the yarn under controlled tension to a fluid twister positioned between a feed point and a takeup point, subjecting the yarn to the twisting action of the said twister while simultaneously and systematically varying the rate of twisting, and immediately thereafter forwarding the as-twisted yarn to the said takeup point at a positive tension less than the tension necessary to remove the imparted twist. The jet of fluid striking the yarn momentarily separates the filaments in the bundle, thereby subjecting the individual filaments to the twisting action of the jet resulting in these filaments twisting upon themselves and about adjacent filaments and groups of filaments. In preferred embodiments of this invention, the rate of twisting is varied by the intermittent application of unidirectional twisting or by alternately twisting in opposite directions, but the rate may be varied by continuous unidirectional twisting with intermittent variation of yarn speed and/ or tension, or with the intermittent upstream application of plasticizing and/ or sizing agents. This process makes possible for the first time the production of a stable alternating-twist yarn having successive bundle segments of S and Z twist, the net sum of all such twist being substantially zero.

By the term stable alternating-twist yarn, as used herein, is meant a yarn characterized by successive seg ments of alternating S and Z twist and which not only opposes forces tending to remove the alternating-twist but tends to return to the alternating twisted configuration after applied tension, sufiicient to remove the twist, is released, and does return to the twisted configuration to a substantial degree. The alternating-twist is stable even though the yarn is completely free of foreign materials such as setting agents, adhesives, and the like, the individual filaments being free to move over one another in the yarn bundle. Of course, these alternating-twist yarns may be set with heat or other agents or treated with sizes, plasticizers, or partially melted and then solidified to cohere adjacent filaments or otherwise treated if desired, but none of these treatments is necessary to produce the alternating-twist yarns of this invention. The stability of the yarn appears to arise solely due to the twisted configuration of individual filaments and/ or groups of filaments produced during treatment of the yarn by a twisting jet of fluid and to frictional constraint between adjacent filaments within the yarn bundle. The twisting of individual filaments and groups of filaments within the yarn is random both in direction and amount and independent of bundle twist.

:The process of this invention permits production of a stable twisted yarn in a rapid and continuous manner at speeds comparable to or greater than conventional drawing and spinning speeds, thereby allowing combination of these separate steps into a single, efficient, highspeed operation. The alternating-twist yarn can be used in the place of conventional true twisted yarn in a wide variety of applications.

In its simplest embodiment, the apparatus of this invention comprises, in combination, a fluid twister and means for passing yarn through the twister at controlled tension. The fluid twister comprises a yarn passageway which is a smooth curved concave surface in combination with one or more fluid conduits positioned to direct a stream of fluid circumferentially about the inner periphery of the concave surface. The yarn passageway may be integral with the fluid conduits, or the latter may be spaced apart from the yarn passageway but in position to direct fluid substantially tangentially to the inner periphery of the curved concave surface at some point. The axis of fluid flow must not intersect the axis of the yarn passageway, but it may lie in a plane substantially perpendicular to the longitudinal axis of the concave surface, or in a plane inclined up to about 75 degrees or more from this perpendicular in order to exert forward movement or breaking action upon the yarn in addition to twisting motion. There may be a plurality of conduits directing fluid flow about the periphery of the concave surface, and these conduits may be spaced longitudinally or circumferentially or both about the yarn passageway. Naturally, in order to obtain the highest rate of twisting, all fluid conduits, where there is a plurality, should be directed in substantially the same tangential direction. It is not necessary, however, that the longitudinal axes of all the fluid conduits lie in the same or parallel planes with respect to the axis of the yarn passageway. One or more of a plurality of fluid conduits may have axes perpendicular to the axis of the yarn passageway while one or more others may have axes inclined to impart forward or twisting motion to the yarn while other fluid conduits may have axes inclined backward along the axis to partially inhibit the passage of the yarn therethrough. In the case where there are a plurality of fluid conduits supplying fluid to the yarn passageway, it may be desirable to provide one or more exit ports along the yarn passageway, and these may be positioned at any convenient points.

The product, process, and apparatus of this invention can be more readily understood by referring to the attached drawings, wherein:

FIGURE 1 illustrates an alternating-twist yarn of this invention.

FIGURES 2 through 6 show various embodiments of fluid twisters which may be utilized in the present invention. Additionally examples of fluid twisters which may be used appear as FIGURES 1-31 in U.S. Patent No. 3,009,309, issued November 21, 1961, to Breen et al., of which this application is a continuation-in-part.

FIGURES 7 through 9 illustrate various assemblies in which the pneumatic twister of this invention may be utilize to twist yarn continuously or to produce novelty yarns.

FIGURE 10 illustrates a sheaf-yarn.

FIGURE 11 is a graph showing various characteristics of an alternating-twist yarn.

FIGURE 12 illustrates twist doubling.

FIGURE 13 shows the structure of a stable alternatingtwist yarn when the yarn bundle is forceably divided.

FIGURES 14-17 are graphs showing twist retentivity of yarns of this invention.

FIGURES 2 through 6 and FIGURES l-31 in US. Patent No. 3,009,309 illustrate the manner of interception of a yarn passageway 51 by one or more fluid conduits 52 and exhaust ports 56 and also show various forms which yarn passageway and fluid conduit may assume. like numbers appearing in the various figures represent similar structures although the shape or form of the structure may vary from one figure to the next. For example, in each of FIGURES 2 through 6 the yarn passageway is numbered 5 1. Similarly, the fluid conduit is numbered 52 in each of the figures and so on.

FEGURES 2 and 5, which illustrate representative fluid twisters useful in this invention, contain axial yarn passageway 51 which, in this embodiment, is substantially cylindrical in form throughout its length. A conduit for fluid 52 intercepts the yarn passageway at 53 and is positioned so that the longitudinal axis of the fluid conduit 52 does not intersect the longitudinal axis of yarn passageway 51, as shown in FIGURE 2. When gas under pressure is passed through fluid conduit 52 so that it reaches at least /2 sonic velocity upon emerging into the yarn passageway 51, the force of the gas opens up the yarn and separates the filaments momentarily while simultaneously applying suflicient torque to any yarn in the yarn passageway to produce a high rate of twisting. At relatively high fluid velocities, less dense fluids can be employed to obtain substantially the same torque produced by a higher density fluid traveling at lower velocity. Fluid may be supplied to the fluid conduit 52 by any convenient means. Preferably, the yarn passageway will have rounded edges at both ends to minimize tearing of the yarn bundle, and, in accordance with one embodiment shown in FIGURES 2 and 3, the yarn passageway is widened by bevels 55 at the yarn entrance and exit ports. Naturally, it is not necessary that these widened portions of the yarn passageway be symmetrical or even similar in shape.

In some instances as, for example, when the yarn passage is of substantial length, it is desirable that the yarn passageway contain one or more fluid exhaust ports in order to facilitate removal of fluid from the yarn passageway. According to a particularly preferred embodiment, the fluid twister may be designed to provide for ease in stringing-up a threadline by providing a string-up slot running the entire length of the yarn passageway. The string-up slot may simultaneously serve as an air conduit or exhaust port, as desired. Any of the fluid twisters can be adapted to provide string-up slots. FIGURES 4 and 5 show views of a twister having in addition the air-curtained string-up slot 57. FIGURE 6 shows a double vortex twister which is capable of alternate twisting while utilizing a unidirectional air supply. This latter twister is used in combination with conventional recipr ocating traverse means. These twisters will be discussed in greater detail hereinafter.

The above-described fluid twisters are suitable for twisting a large variety of filamentary strand structures, including staple or continuous multifilament yarn, monofilaments, thread, fibers, roving strands, and the like. Yarn will be employed throughout the instant disclosure as exemplary of all such structures, since in the twisting of yarn the invention has its greatest utility. The yarn or the like structures may be composed either partially or entirely of synthetic polymeric materials, such as the polyamides (nylon), e.g., poly(e-caproamide) and poly(hexamethylene adipamide); polyesters, e.g., poly(ethylene terephthalate); acrylic polymers, such as poly(acrylonitrile) and/ or the many copolymers thereof; vinyl polymers, e.g., poly(vinyl chloride), poly(vinylidene chloride) or copolymers thereof; hydrocarbon polymers, such as polyethylene or polypropylene; and so on. The composition may be based on naturally occurring materials, including the cellulose esters, regenerated cellulose (rayon), regenerated protein, cotton, wool, silk, etc.

In twisting yarn with a fluid jet the twister is usually positioned bet-ween an upstream feed point, e.g., a set of pinch rolls or other suitable snubbing means, and a downstream takeup point, e.g., a windup package. Yarn is fed continuously from the feed point, through the twister, and thence to the takeup point. When fliuid is supplied to the twister, the yarn is twisted in opposite directions, up and downstream from the twister. Downstream twist is accumulated beyond the takeup point, e.g., on a package, while upstream twist of an equal amount but opposite direction is accumulated between the twister and the feed point. If such twisting is maintained constant, the point is rapidly reached where the upstream twist is accumulated to an extent sufficient to counteract the action of the twister, i.e., upstream twist commences to pass through the twister, leading to the cancellation of the applied downstream twist. Mechanically speaking, at this point the upstream twist countertorque becomes equal to the applied torque of the twister. This condition, conveniently termed equilibrium twisting, usually results in the winding of zero-twist yarn past the takeup point, as in the case of the prior art false-twisting discussed hereinabove, or complete breakdown of the yarn line, twist doubling, etc. However, by virtue of the present invention it becomes possible to avoid such a condition of equilibrium twisting by systematically varying the rate of twisting, in accordance with any one of the several useful embodiments of this invention.

According to this invention, a stable alternating twist yarn is prepared by utilizing a fiuid twister in the manner described in the foregoing while simultaneously and systematically varying the rate of twisting. A preferred way to provide suitable variation of the rate of twisting comprises intermittent application of twisting fluid. Thus,

after upstream twist is accumulated to a predetermined extent, preferably before the onset of equilibrium twisting, the supply of fluid to the twister is diminished or interrupted completely to allow some or all of the accumulated upstream twist to pass downstream to the takeup point, after which the flow of fluid is resumed, and the cycle repeated. Such an intermittent twist-notwist action, when suitably timed with respect to yarn speed permits the winding and packaging of yarn having good uniformity of twist periodicity and level. Of course, the on-off cycles need not be of equal duration. The intermittent (pulsating) application of unidirectional twist is often preferred for the purposes of the present invention.

Another preferred way to provide suitable variation of the rate of twisting comprises intermittent application of twisting in opposite directions. Thus, when an equilibrium twisting condition is approached, twisting in the opposite direction is initiated, permitting in effect upstream twist to pass downstream to the takeup point. Such a method tends to be relatively insensitive to timing of the twist cycles, and results in yarn of good uniformity. The fluid twisters of FIGURES 4, 5, and 6 are used for intermittently opposed twisting.

A stable alternating-twist yarn can also be produced with continuous unidirectional application of twisting by systematically varying the tension in the yarn, the speed of the yarn, or by intermittent upstream setting, e.g., by the intermittent application of heat or size to the running yarn. A decrease in yarn tension avoids equilibrium twisting by permitting an increase in upstream accumulated twist and hence a corresponding increase in downstream twist being forwarded to the takeup point. Conversely, an increase in yarn tension permits the accumulated'upstream twisting to pass through the twister and pass the takeup point. By systematically varying the yarn tension above and below a reference level, an alternating-twist yarn is produced. The effectiveness of this method is dependent upon the range of tension variation, its period with respect to the yarn speed, and the effect of varying tension on the twister. In a similar manner, by systematically varying yarn speed, an alterhating-twist yarn is also produced. A decrease in yarn speed permits an increase in upsetream twist accumulation; conversely, an increase in yarn speed permits upstream twist to pass through the twister to the takeup point. Yarn tension is conveniently varied by using the means indicated at 31 in FIGURE 9. Yarn tension and speed may be concomitantly varied to increase the effectiveness of the separate operation. Note that when conventional reciprocating traverse means are employed in the windup system (package 18 and drive roll 19), there at once occurs a varying tension in the yarn line sufficient to produce an alternating-twist yarn of average twist level of 0.8 or more turns per inch. This effect is greatly increased by using the fluid twister of FIGURE 6, whereby the traverse stroke causes the yarn alternately to be twisted in yarn passageway 51a (clockwise twisting) and yarn passageway 51b (counterclockwise twisting). Fluid is supplied to both passageways simultaneously through the common fluid conduit 52. Using the fluid twister of FIGURE 6, the associated traverse means may be located either upstream from the twister, e.g., at 31 in FIGURE 9, or downstream therefrom, e.g., at the winding 1-19. Upstream traversing may also be used to provide intermittent sizing or setting with the elements 32 and 33, respectively, of FIGURE 9 located in a fixed position downstream from the reciprocating traverse means located at, e.g., 31. Numerous other apparatus and process possibilities will readily occur to those undertaking the practice of this invention. However, the most versatile of these methods is intermittent unidirectional or two-directional twisting due to simplicity of apparatus ease of operation under a wide variety of conditions of yarn speed and tension, and uniformity of the product so produced.

Twisting in accordance with this invention, whether it be intermittent unidirectional or alternately in opposite directions, leads to yarn having segments of twist in one direction, each positioned between segments containing opposite twist. All segments usually contain about the same length of yarn, and about the same amount of absolute twist. The net twist in the yarn is essentially zero, that is, the total 6 twist is equal to the total Z twist. The resulting yarn is called a stable alternatingtwist yarn. An exaggerated alternating-twist yarn is shown in FIGURE 1.

It is well known in the art of twisting that when several bundles of yarn are separately twisted and then combined, the resulting structure after twisting exhibits greatly enhanced stability. This effect is readily ohserved in, e.g., ropes, cables, hawsers, and the like. It is by a similar mechanism that the surprising degree of twist retentivity of the instant yarns may be explained. Thus, in the process of this invention, a fluid stream not only imparts a high-speed rotation to the yarn bundle, but also causes individual filaments and/or groups of filaments within the yarn bundle to be separately twisted. Such filament twisting, in addition to the yarn bundle twisting, is observed in the product of this invention.

FIGURE 11 shows graphically the lengthwise variation in twist along the length of a segment of an alternatingtwist yarn of this invention wherein ordinate 08 indicates level of S twist and ordinate oZ indicates level of the Z twist at any point along the yarn length, i.e., the abscissa 0L. At the initiation of twisting (at 0), the S twist level rises rapidly to a maximum (a), then, approaching equilibrium twisting, falls off towards b. Twisting is stopped or reversed at b, allowing the upstream accumulation of twist to pass downwstream and onto the beam. Such practice results in Z twist rising to its maximum twist level at c, then, again approaching equilibrium twisting, falling off towards a, at which point twisting in the 8 direction is initiated, and the process commencing at o is repeated. By suitable variation of processing conditions, the curve of FIGURE 11 can be made to assume a variety of proportions which, of course, need not be symmetrical. Note that as the twist level rises from 0, the yarn cross section approaches substantial circularity, whereas zerotwist yarn (at has a ribbon-like cross section.

Characteristics useful for describing a stable alternating-twist yarn are the twist period, maximum twist, and average twist. Twist period or cycle length is the distance along the threadline that contains a complete section of both 8 and Z twist. A length of yarn containing twist in but one direction (8 or Z) is described as the increment length of twist. The average twist level is defined as the absolute numerical average of twist per unit length, taken over a representative sample length of yarn (several twist periods), regardless of twist direction. Maximum twist is the largest amount of twist (in turns per inch) encountered in an S or Z twist section. The three parameters are interrelated by the generality that average twist approaches the maximum twist value as twist period increases. The curve of FIGURE 11 tends to flatten as the ratio decreases (see Equation 1). Referring to FIGURE 11, the twist period is the length of segment 0d; increment length of twist is the length of segments 0b and bd; maximum twist is indicated at a or c, and average twist is given by dotted line oL'.

FIGURES 7 through 9 show various assemblies in which the fluid twister may be used to twist yarn continuously into a stable alternating-twist yarn. FIGURE 7 illustrates schematically a string-up assembly for twisting yarn immediately after spinning and prior to packaging. Filaments 11 issue from spinneret 12, converge at guide 13 into yarn 14, and finish is optionally applied (means not shown) prior to passing the nip rolls 15, which serve as snubbing means and the feed point for twister 16. After twisting, yarn 14 passes idler roll 17 and then to the takeup point, backwindable package 18 driven by drive roll 19. FIGURE 8 illustrates schematically a string-up assembly whereby yarn is twisted immediately after drawing and prior to packaging. In accordance with this embodiment, undrawn yarn 14 is withdrawn from package 30, passes through pigtail guide 21, then is passed in multiple wraps about driven feed roll 22 and its associated separator roll 23. In a highly preferred embodiment, yarn is supplied directly to guide 21 from a spinning position (see FIGURE 7) rather than a package. From feed roll 22 the undrawn yarn makes one or more wraps about a snubbing pin 24 and is drawn in frictional contact therewith under the urging of draw roll 25 and its associated separator roll 26. Draw roll 25, of course, has a higher peripheral speed than feed roll 22, whence the yarn is elongated to several times its original length. From draw roll 25, which serves as the feed point, the yarn passes twister 16, is twisted as directed hereinabove, then passes idler roll 17 to the package 18 driven by drive roll 19. Twisting in both FIGURES 7 and 8 may be either intermittent unidirectional or two-directional; uniform alternating-twist yarn is wound onto package 18 in both cases. Conventional traversing means (not shown) are usually associated with both windup assemblies.

FIGURES 2 and 3 show section and end views of a typical fluid twister which may be employed in the processes of FIGURES 7 and 8. Twister 50 comprises cylindrical yarn passageway 51-56, with enlarged exhaust section 56, beveled section 55, and twisting section 51, the latter being tangentially intercepted at 53 by the fluid conduit 52 in a plane normal to the axis of the yarn passageway. In operation, fluid passing through conduit 5'2 intercepts the yarn 14 in twisting section 51 and imparts thereto a twisting action. By periodically interrupting the supply of the fluid to the twister, intermittent unidirectional application of twist described in the foregoing is achieved. With reference to the diagrammatic representation in FIGURE 11, fluid is supplied to the twister during passage of a segment of yarn having length 017. Fluid supply is interrupted for a yarn length bd. Enlarged exhaust section 56 of the twister 59 serves to facilitate the release of exhaust twisting fluid with minimum interaction with the yarn. Beveled section 55 serves to guide the yarn into twisting section 51, and serves to minimize yarn damage. Alternatively, the twisters of FIGURES 4 or 5 may be used. Using such a twister, twisting in one direction occurs during passage of yarn segment ob (see FIGURE 11). At b, the direction of twisting is reversed by supplying fluid to the opposed conduit, thereby twisting yarn segment bd in a direction opposite to that of 0b, resulting in production of an alternating-twist yarn 0d (FIGURE 1). Fluid is supplied to a twister intermittently or to opposed fluid conduits alternately by use of suitable rotary valve means or the like, suitably interposed between the fluid source and the twister proper.

FIGURE 9 illustrates a string-up assembly whereby an alternating twist yarn is produced continuously from either lament or staple yarn by varying the rate of twisting through continuous or intermittent setting and/or sizing, or by methods involving varying the tension in the yarn. In the schematic drawing of FIGURE 9, yarn 14 supplied from either a spinning position, such as shown in FIGURE 7, or from a package, such as shown in FIGURE 8, passes guide 13 or 21, then to nip rolls 15. Alternatively, staple roving 27 unwound from package 28 passes in sequence through a trumpet guide 29, the drafting rolls indicated at 39, and nip rolls 15. The strand 14 or 27, as the case may be, then encounters the tension varying means 31, size applicator roll 32;, setting means 33, and the eyelet guide 34; then is twisted by fluid twister 16 and passes to package 18 driven by roll 19. Tension varying means 30 may be a bell crank, a vibrating tension gate, reciprocating means, an elliptical roll, or the like. Size applicator roll 32 revolves in a bath of size or adhesive solution, and is arranged so that size may be applied continuously or intermittently to strand 14 or 27. Setting means 33 may be a hot plate or other suitable heating means such as a hot pin or pipe, a steam tube, an oven, hot liquid bath, infrared radiator, and the like. The yarn may be plasticized in the absence of heat as, for example, with solutions of chemical plasticizers or similar materials. When plasticizing is affected with heat, the temperature of the heating medium must be regulated so that the yarn temperature does not reach the melting point of the yarn material. It is quite possible, of course, that the heating medium temperature or source of heat be above the melting point of the yarn if yarn speeds are such that the yarn temperature is maintained below its melting point. Temperatures lower than the second-order transition temperature of the yarn material should usually not be employed because, under these conditions, any setting of the filaments is not permanent and utility of the product is reduced. Setting means utilizing dry heat may be used in combination with size applicator 82 to facilitate drying the size solution applied thereby. Eyelet guide 34 serves to center the strand 14 or 27 in twister 16 in the case where the strand tension is varied by upstream displacement. Twister 16, when used in the various arrangements permitted with the apparatus of FIGURE 9, may be operated continuously without changing the direction of twisting.

Utilizing the apparatus of FIGURE 9, but in the case where no adhesive or size is applied to roving 2'7 and plasticizing is also omitted, the product produced by the twisting action of the fluid twister on the roving is a sheafyarn, such as illustrated in FIGURE 10. The product is called a sheaf-yarn because it resembles sheaves of wheat or, more exactly here, sheaves of staple yarn attached end to end and tied at random intervals along its length by staple fibers twisted firmly about the circumference thereof. Intermediate the tightly bound portions of the yarn the staple fibers are substantially parallel to one another.

In utilizing the assembly of FIGURE 9 and processing staple roving as above described but applying an adhesive solution to the roving prior to continuous uninterrupted twisting but omitting any plasticizing of the roving prior to such twisting, there is obtained an alternating-twist staple yarn having an appearance somewhat similar to the twisted yarn shown in FIGURE 1 with the exception that FIGURE 1 is directed to an alternating-twist continuous filament yarn. An alternate twist staple fiber yarn has essentially the same configuration but with a somewhat more fuzzy appearance due to the multiplicity of fiber ends protruding from the fiber bundle. When the assembly of FIGURE 9 is operated with a plasticizer, for example, a heat plasticizer, but without application of adhesive, the yarn product has somewhat greater bulk but somewhat less stability than the yarn product obtained with adhesive application. When adhesive application alone is utilized in the absence of any plasticizing means, it is essential that the adhesive be sufficiently volatile so that it will be set (by polymerization or solvent volatilization) during the interval between application of the adhesive solution and entrance into the fluid twister. The air discharge from the fluid twister accelerates the setting of solvent based adhesives. However, the most efficient operation involves adhesive application in combination with heat-setting. The above considerations are equally valid as applied to continuous filament yarn. Note that the twist applied to projected ends of staple fibers is a true twist, and the whipping and twisting of these ends about the yarn bundle make it very coherent. By applying this process to staple roving, a yarn can be spun at speeds much higher than those obtainable on a conventional spinning frame. By varying the processing elements, the product can be varied all the way from a conventional spun yarn to a highly bulked stretch-type yarn. When twisting in accordance with this invention, staple roving, plyed roving, spun yarn, and the like may be twisted through the point of zero-twist, without pulling the bundle apart, a feat heretofore impossible.

Air at room temperature is preferred for twisting yarn in the fluid jet device of this invention, but the air may be heated or refrigerated, if desired. Low pressure steam may also be used where its plasticizing action, if any, is not harmful. Other gases substantially inert to the yarn, such as carbon dioxide, nitrogen, and the like, may be utilized, if desirable. The invention is illustrated using air as a fluid because air is preferred in carrying out the process of this invention, but any inert fluid is suitable providing its plasticizing action, if any, is less than that of any upstream plasticizing step utilized. In order to operate the process in accordance with the invention, it is necessary that the fluid, for example, air, immediately prior to impinging upon the yarn reach a velocity of /2 sonic velocity or more, so that depending on the diameter of the yarn passageway, twisting speeds of between about 200,000 and about 2,000,000 revolutions per minute are easily obtained. For this purpose, air at a pressure of at least about 10 psig. is usually sufficient, with a pressure about p.s.i.g. or more preferred, when operating at normal yarn tensions. Even lower pressures may be employed in those cases where the yarn tension is of a low order.

It is preferred that yarn tension be of a low order, and tensions less than about 15 grams are desirable in most applications. Lower tensions, say between about 0.1 and about 10 grams, are preferred, and for the most efiicient twisting action at the highest twisting rates and yarn throughout, tension of the yarn should be maintained between about 0.5 and about 5 grams. Tension during twisting should be sufficient to prevent twist doubling, as illustrated in FIGURE 12.

Whereas the average twist level in an alternating-twist yarn is controlled primarily by tension and fluid pressure, the twist period is determined by the duration of twisting, i.e., the time interval during which twist of one direction is being accumulated in the yarn as it passes the takeup point, which, in turn, depends on the method by which the rate of twisting is varied. Accordingly, the duration of twisting is related to the frequency of intermittency of twisting direction or duration, the frequency and duration of upstream size or setting, and the frequency and range of tension or speed variation. Thus, the duration of twisting determines the length of the yarn segment over which twist of a given direction is accumulated, and hence also determines the twist period except during conditions of equilibrium twisting. During equilibrium twisting, of course, zero-twist yarn is packaged. To avoid packaging of zero-twist yarn, the duration of twisting should be adjusted to less than the time required to establish an equilibrium twisting condition. Although there exists no theoretical upper limit for the twist period, or more precisely, the increment length of the twist, there is a practical upper limit, determined by the distance between the twister and the first upstream snubbing guide. A snubbing guide tends to inhibit the further upstream accumulation of twist. Therefore, twist is confined to the yarn segment between such a snubbing guide and the twister, and since only a certain amount of twist may be accumulated before the upstream twist counteracts the twister (at initiation of equilibrium twisting), the upper limit of the period is thereby limited. The above variables are related through the equation where S is the yarn speed, L the upstream distance from the twister to the first snubbing guide, T is the twisting speed, t is the upstream twist level, and D is the duration of twisting, i.e., time interval following the initiation of twisting to the point where i is achieved. Since the equilibrium upstream twist level is given by the expression T/S, it is possible to determine D so that 1,, does not exceed about 0.9 T/S, thereby avoiding a condition of equilibrium twisting and, therefore, permitting production of an alternating-twist yarn having excellent uniformity of twist level and twist period. D is dependent upon the ratio S/L The practical significance of this relationship is that as the S /L ratio increases, i.e., as the yarn speed increases or the upstream distance decreases, the time after initiation of a given twisting cycle required to achieve equilibrium twisting decreases, hence D under such conditions should be correspondingly reduced to avoid the production of zero-twist yarn. Where D exceeds the time required to achieve equilibrium twisting, an alternating-twist yarn is produced containing sections of zerotwist yarn between sections of S and Z twist, respectively.

The nature of the yarn being twisted influences the rate of twisting. The ratio of yarn diameter to the diameter of the yarn passageway of the twister determines to some extent the nature (direct vs. reverse twisting) and efficiency of twisting; the ratio of the two quantities in that order should be from about 1:2 to about 1:10, and preferably about 1:4. The torsional modulus of the yarn determines the twist level at a given tension value. Thus, when comparing the upstream twist behavior of 70 denier, 34 filament yarns composed of poly(hexamethylene adipamide) and poly(ethylene terephthalate) during a condition of equilibrium twisting, it is observed that at comparable tensions (6 gm.), about 30 t.p.i. versus 50 t.p.i., respectively, are obtainable under the same twisting conditions. Moreover, at reduced yet still comparable tensions (2 gm.), and with the same twisting conditions, twist doubling (FIGURE 12) is seen in the latter yarn, whereas none is observed with the former. The elfective torsional modulus of the yarn may be diminished by the application of heat and/ or other plasticizing means. Thus,

'tain demands upon associated equipment.

under the same condition of twisting referred to above, and at 2 grams tension, the same poly(ethylene terephthalate) yarn may be twisted at 180 C. to more than 100 t.p.i. without the occurrence of twist doubling. Yarn may be conveniently heated during processing by utilizing the means indicated at 33 in FIGURE 9.

The nature of the process of this invention makes cer- As mentioned an alternating twist is trapped or confined by a snubbing-type guide, e.g., pinch rolls, nip rolls, and the like. Twist ordinarily cannot pass upstream from such a guide. In addition, such guides as the yarn may encounter downstream rrom the twister preierably should be of the nonsnuboing variety, such as eyelet guides, comb guides, and freely rotating idler rolls. The roll 17 in FIGURES '79 is of such freely rotating operation. Where downstream tension variation is used to produce alternating twist, the roll 1'7 or its equivalent should be omitted so that such variations are relayed to the twister without diminution or damping. Upstream from the twister, the location of the first snubbing guide determines the maximum increment length of twist. Referring to FIGURES 7 and 9, nip rolls serve in that capacity; in FIGURE 8, draw roll satisfactorily contains the upstream twist accumulation. Optionally, eyelet guides may be positioned approximately the same distance upstream and downstream, respectively, from the twister to permit accurate coaxial entry and exit of the yarn to and from the twister. Such practice tends to minimize fluctuations in the yarn line due to the influence of fluid exhausting from the twister. One such guide is shown at 34 in FIFURE 9. Insofar as the distance L from the twister to the takeup point is concerned, it is preferred that that value be minimized. It has been shown that as the ratio L /L increases, the downstream twist level, as measured at the takeup point also increases with respect to the maximum obtainable upstream twist level. A high value of L /L is achieved by positioning the twister at about the takeup point, e.g., the twister could be made a part of the traverse guide.

The alternating-twist yarn of this invention may be backwound in such a manner as to remove or retain twist, as required, although the structure is unusually retentive in most operations. Twist can be removed if the free suspended length of yarn during backwinding or any subsequent textile operation is allowed to exceed the twist period, while at sufflcient tension. By free suspended length is meant the length of running yarn tensioned between two snubbing-type guides, e.g., between a package and a snubbing guide. If shorter lengths of yarn are freely suspended, twist removal is incomplete. Since some twist is contained by acute snubbing, when such a guide is encountered during backwinding, some twist will tend to accumulate and be concentrated upstream from such a guide. Twist of the opposite direction will also run into that region, leading to some twist cancellation. Accordingly, by suitable positioning of snubbing guides with respect to the package during backwinding, twist removal may be accomplished. Completeness and efliciency of alternating-twist removal is governed by the tension applied and the free-suspended length of yarn.

If it is desirable that twist be completely retained during backwinding, it is obvious that the above-mentioned conditions are to be avoided. Therefore, to retain twist during backwinding or during any subsequent textile operation, the free suspended length of yarn should be kept low, the use of acute snubbing guides or the like means avoided, and tension should be maintained at the lowest suflicient level. The retention of twist may be further assured by utilizing a higher average twist level initially, or by increasing the period, or both. Twist may also be set by twisting the yarn in the plastic state (via heat or residual solvent) followed by cooling, by slashing the as-twisted yarn, or by the application of size or an adhesive during twisting. A desirable method to insure residual twist retention is to increase the average twist level. This is accomplished in pneumatic twisting by increasing the fluid pressure or reducing the yarn tension or both. Increasing the average twist level is preferred over increasing the period, since by the latter iethod the reversal length between segments containing twist in opposite directions tends to increase. Such exaggerated sections of yarn having little or no twist are subject to the same diflicultics during backwinding, as is zero-twist yarn.

A surprising degree of twist retentivity is observed with the yarns twisted in accordance with this invention, believed due to the twisting of individual filaments and groups of filaments, in addition to twisting of the yarn bundle. As a result of this, twist is retained during such textile operations as slashing and weaving, provided that excessive tensions are not encountered.

The process of this invention is illustrated by the following examples.

EXAMPLE 1 An alternating-twist yarn is prepared by intermittent twisting in opposite directions using the fluid twister of FIGURES 4-5. The yarn is twisted immediately after spinning, using the string-up of FIGURE 7. Both fluid conduits 52 of the twister are 0.0225 inch in diameter, and enter the yarn passageway 51 at about its lengthwise midpoint. Yarn passageway 51 is 0.030 inch in diameter and 0.250 inch in length. The axis of the fluid conduits 52 are inclined 30 from the horizontal, are apart, and intersect the yarn passageway 51 at a common point located at the uppermost vertical point of its circular cross section, i.e. intermediate the sides of the string-up slot 57, which is 0.005 inch wide. Air is the twisting fluid, and is supplied alternately to each of fluid conduits 52 by rotary valve means (not shown), which supplies air to each fluid conduit for the same length of time, i.e., air is supplied to one conduit during /2 valve cycle of revolution, then to the other valve during the remaining /2 cycle. The valve speed, in r.p.m., determines the twist periodicity and the time interval during which twist of one direction is being imparted to the yarn.

The above apparatus is used to twist alternately a 75 denier, 24 filament yarn composed of cellulose acetate. The spinning speed, i.e., the speed of the yarn during twisting is 620 y.p.m., and yarn tension is 10 grams. The rotary valve speed is 510 rpm. The effect of varying air pressure is shown in Table I.

Table I Air Flow (cubic feet/min.)

Air Pressure (turns/inch) The twist period is uniform (36 inches) throughout this test. When the valve speed is 450 r.p.m., the following results are obtained:

Table II Air pressure (lbs/in?) Average twist (turns/inch) 20 0.7 30 16 4O 2 4 45 3 0 When twisting denier, 40 filament cellulose acetate yarn at 517 y.p.m., tension 10 grams, and a valve speed of 450 r.p.m., the following results are obtained:

13 Table III Air pressure (lbs/in?) Average twist (turns/inch) 15 0.6 30 1.3 40 2.0 5

The twist period is uniform (27 inches) throughout. When the valve speed is increased to 900 r.p.m., the following results are obtained:

Table IV Air pressure (lbs./in. Average twist (turns/inch) 30 3 4O 0 5 50 0 8 When 55 denier, 18 filament cellulose acetate yarn is twisted at 690 y.p.m., tension 5.5 grams, 450 r.p.m. valve speeds, the following results are obtained:

is twisted at 617 y.p.m., 5.5 grams tension, and 2.5 p.s.i.g. air pressure. The following results are obtained:

Table VI Valve Speed (r.p.rn) Period Length Average Twist (inches) (t.p.i.)

7G 2. 3 3G 1. 4 20 O. 9 18 0.7

Average twist level in an alternating-twist yarn is determined by making twist counts on successive short lengths (1-3 inches) of yarn and averaging over the total length of yarn, approximately 72 inches) regardless of direction of twist. Algebraically, the net twist in an alterne ting-twist yarn is zero. The period length is measured as the distance between segments of yarn containing both 8 and Z twist, or merely as the sum of the respective increment lengths.

The results in Tables I-VI show the effect of varying air pressure on the average twist level in the various yarns tested. Also, the dependence of average twist level on yarn denier, valve speed (Table VI), yarn speed and tension. The dependence of twist period on valve speed is seen in Table VI. In this example, drive roll 18 of the windup is self-traversing.

Using the same twister as described above, a 70 denier, 34 filament sample of poly(hexamethylene adipamide) yarn is twisted at the high speed of 2150 yards per minute. Tension is controlled between 12 and 15 grams, the following results being obtained:

Table VII Rotary Twist Average Air Pressure (p.s.i.g.) Valve Period Twist Speed (inches) (t.p.i.) (r.p.m.)

Using the same twister, the above nylon yarn is twisted 75 immediatel following the drawing operation, using the 14 string-up of FIGURE 8. The yarn The following results are obtained:

speed is 940 y.p.m.

Table VIII Rotary Twist Average Air Pressure (p.s.i. g.) Valve Period Twist Speed (inches) (t.p.i.) (r.p.m.)

A stable alternating-twist yarn of 75-24 cellulose acetate is passed through a Saco-Lowell Positrol slasher without slashing fluid so as to simulate the tension and suspension conditions of ordinary slashing while eliminating slashing fluid which would tend to hold the twist in the yarn. The yarn passing through the slasher is subjected to gradually increasing tension and the changes in average twist level noted. The results are as follows:

Table IX Tension grams/ denier): Average twist level (t.p.i.) 0 (approx.) 2 10 1 20 1 30 0.5

The twist retentivity of the alternating-twist structure of the yarns of this invention is illustrated by electrically recorded graphs of FIGURES 14-17, in which twist retentivity is indicated by the amplitude of the wave forms at tensions of 0, 10, 20, and 30 grams, respectively.

EXAMPLE 2 An alternating twist yarn may be prepared by the intermittent application of unidirectional twisting. The fluid twister of FIGURES 2-3 is employed, and yarn is twisted immediately after drawing, using the string-up of FIGURE 8. The dimensions of the twister are as follows:

Length Diameter Exhaust Section 56 0.24 inch each--. 0.150 inch. Beveled Section 55. bev l Twister Section 51 0.245 inch 0.050 inch. Fluid Conduit 52 0.020 inch.

T 0.875 inch Air is supplied to the twister intermittently by a rotary valve (not shown) which permits air to flow to the twister during /2 of each cycle of revolution. Valve speed is 250 r.p.m. A11 840 denier, filament yarn of poly- (heXarnethylene adipamide) is twisted at 500 y.p.m., 35

grams tension. Results obtained at several pressures are indicated in Table X.

similar relationship between air pressure and average twist to that shown in Example 1. As the tension in the yarn decreases, the average twist level rises.

Alternating twisting in a fluid jet improves the quality of yarn after drawing, since any broken filaments incurred during drawing the twisted back into the yarn bundle, eliminating subsequent filament stripbacks and wraps. This feature of the instant invention is shown in the following tests made on denier, 40 filament cellulose acetate yarn, intentionally degraded to form loops, broken filaments, and the like defects. The number of defects is counted immediately before and after twisting (using Example 1 twister) to provide a quantitative measure of the quality improvement in the yarn deriving from the twisting process. The yarn is twisted to about 1.5 t.p.i., and gross yarn defects are measured using the detector shown in US. 2,841,048 to Duncan et al. These results are shown in Table XI.

Using the string-up of FIGURE 9, viscose rayon staple filament yarn issuing from the drafting rolls 30 at 50 y.p.m. is passed over applicator roll 32 and a heated plate 33 prior to entering pneumatic twister 16. The applicator rolls apply a size [aqueous poly (vinyl alcohol) emulsion] to the twisted yarn. The hot plate dries the size and fixes the yarn in its twisted configuration. Due to the combination of size and heat, the twist is fixed so tightly that some of the twist passes through the twister unaltered, with the result that opposite hand twist appears in portions of the yarn leaving the twister and the yarn has the appearance illustrated in FIGURE 1.

The yarn is composed of 1.5 d.p.f., 3 inch staple fibers. A twister of the multiple conduit type, with fluid conduits 52, each of 0.031 inch diameter, and yarn passageway 51 of 0.063 inch diameter. Twisting, therefore, is continuous and unidirectional, The air pressure is 30 p.s.i.g. The hot plate 33 is 30 inches long, and is maintained at 280 C. which is sufiicient to dry the size. The product is an alternating-twist staple yarn having an average twist level of about 3 t.p.i. The twist period of this yarn tends to be irregular in this method. Similar results are obtained with filament yarn.

EXAMPLE 4 The apparatus of FIGURE 9, employing the fluid twister of FIGURES -16, is used to twist 70 denier, 34 filament poly(ethylene terephthalate) yarn, taken from supply package 20. The twister has 5 fluid conduits, each of 0.031 inch diameter, and 0.047 inch diameter yarn passageway. The twister is continuously fed air at a pressure of 30 p.s.i.g. A 13-inch hot plate 33 is used, the temperature being maintained at 270 C. Yarn is fed through nip rolls 15 and 150 y.p.m, and is taken up at the windup at 128 y.p.m. Yarn tension is 3 grams. The fluid twister is slightly misaligned with respect to the direction of travel of the threadline with the result the yarn threadline alternately sticks and slips at the yarn passageway ports so that the yarn is twisted in a pulsating manner. The pulses permit 2 twisted sections of the yarn to pass through the twister without twist removal, with the result that S twisted sections appear in the yarn between the Z twist sections that had escaped the twister action. The resulting alternating-twist yarn has the appearance of a highly twisted crepe yarn and is very twist-lively and very Cohesive- T11? 1 3i twist in the yarn is essentially zero,

that is, there are as many turns of S twist as there are Z twist. The yarn product is illustrated in FIGURE 1.

An alternating-twist yarn is made via a process similar to the above except that instead of misaligning the jet, the nip rolls 15 are eliminated, and a tension gate is placed at 31 and vibrated at a rate of about 20 cycles/sec- 0nd. This causes a corresponding variation in the yarn tension which leads to a variable rate of twisting, and produces a crepe-like cohesive alternating-twist yarn.

EXAMPLE 5 The apparatus of FIGURE 9, employing the fluid twister of FIGURE 1, is used to twist 150 denier, 40 filament textile rayon taken from supply package 20. The yarn passageway is 0.063 inch in diameter, as is the fluid conduit. The twister is operated continuously with 40 .p.s.i.g. air. An eccentric cam having a inch throw is located at 3 1, the applicator roll 32 is used to apply a Ai% aqueous solution of carboxymethyl cellulose, and the hot plate 33 inch x 13 inches) is maintained at 160 C. The yarn tension is controlled at 3-4 grams, the feed speed is 22 y.p.m., and the takeup speed at 16 is 17 y.p.m. Rotation of the eccentric cam at 31 causes size to be applied on alternate 1 /2 inch lengths of yarn, with unsized segments of the same length intermediate each sized segment. The product thus has a period length of 3 inches, and is prepared at an average twist level of 10 t.p.i.

When auxiliary means are used to apply a plasticizer, in this case water, to the unsized segments, the period length remains 3 inches, but the average twist level increases to 20 t.p.i. By extending these techniques, yarns of any desired periodicity can be made having an average twist lever of upward to 100 t.p.i. Also, this method permits preparation of yarns with unequal increment lengths of twist, by adjusting the relative dwell time of the yarn on the applicator roll 32. However, the twist period is unaffected by changes in dwell time and is controlled by the speed of the eccentric, decreasing as the frequency of reciprocation increases. In the case of unequal increment lengths within the period, a necessary consequence is that the twist level will not be the same in each increment. This method of intermittent size application during continuous unidirectional twisting is one of the most effective ways of obtaining very high levels of twist and precise period and increment lengths of twist. This technique also is applicable to staple yarn and drafted staple fibers. Interesting decorative yarns are prepared in the same manner by plying yarns of different colors, then processing according to this example.

EXAMPLE 6 The apparatus of FIGURE 9 less the members 31-34 is used to prepare an alternating-twist yarn during continuous unidirectional twisting by systematic variation of the speed of the yarn. A 70 denier, 34 filament sample of poly(ethylene terephthalate) is taken from supply package 20 through feed rolls 15, twister 16, and thence to the takeup means 18-19. The twister is located as close as possible to the takeup means to maximize the ratio L /L 30 in this case. The motors driving both the feed and takeup rolls are of the variable speed variety and are controlled by a common regulator. The initial feed roll speed is 100 y.p.m., the corresponding takeup roll speed is y.p.m. The secondary feed roll speed is 60 y.p.m., the corresponding secondary takeup roll speed is 51 y.p.m. The rolls operate in synchronous manner intermittently at the two speed levels. The twist period of the yarn is proportional to the frequency of the speed changes with p.s.i.g. air supplied to the twister, the twist lever is about 2 average t.p.i. By the same method, the average level of twist can be varied between 0.5 and 10 average t.p.i. This method can also be effected by using a tension gate in the stead of the feed rolls, a fluid 17 twister, and an elliptical takeup roll, to provide speed variation. The twist level in this latter method depends on the ellipticity of the takeup roll; the twist period depends on its cycling.

EXAMPLE 7 An alternating-twist yarn can be prepared during continuous twisting by systematically varying the tension in the yarn. A 70 denier, 34 filament yarn of poly(hexamethylene adipamide) is passed through a tension gate, the pneumatic twister of Example 6, then to a windup. The twister is located as close to the windup as possible, and is supplied continuously with 90 p.s.i.g. air. The tension gate is intermittently opened and closed, providing an abrupt tension variation from 2 grams (gate open) to 20 grams (gate closed). There results an alternatingtwist yarn with ca. 2 average t.p.i. of twist, at various periodicities depending on the frequency of the tension gate cycle.

In a similar manner, the above twister is mounted on the traverse cam of the windup to provide a higher L /L ratio or" 50, then used to twist 250 denier, 34 filament poly(hexamethylene adipamide). The yarn is fed at 10-0' y.p.m. from a feed roll directly to the twister and windup. The yarn tension is a nominal 10 grams, and the traverse cycle is 4 c.p.s. The product is an alternating-twist yarn of 1.5 average t.p.i.; the twist period is proportional to the traverse frequency. In this method the respective increment lengths of twist tend to be unequal. The tension variation derives from the rapid buildup of tension which occurs at the extremes of the traverse stroke. Twist levels between 0.5 t.p.i. and about 30 t.p.i. can be prepared by this method.

EXAMPLE '8 A 70-34 poly (ethylene terephthalate) alternate twist yarn is subjected to the tensions shown in Table XII at the free suspended lengths indicated with the resultant efiects on the average number of turns per inch in the yarn.

Table XII shows that the alternating-twist yarns of this invention have very surprising twist retentivity particular- 1y when compared with mechanically false twisted yarn which has relatively negligible twist retentivity. One possible explanation for the twist retentivity of the yarns of this invention is the random twist of individual filaments and groups of filaments within the bundle as shown by FIGURE 13 which illustrates the appearance of a typical alternating-twist yarn of this invention when an attempt has been made to separate the filaments transversely. For purposes of this invention it is necessary that the alternating-twist yarn have an average level of twist sufiiciently high enough to provide the yarn with the cohesiveness and runnability of a true twisted yarn having at least 0.5 turn per inch true twist, that is, that the alternating-twist yarn be capable of being processed in a practical commercial process and be suitable for processing in any conventional textile yarn process in which true twist yarn having 0.5 turn per inch is utilized.

1s EXAMPLE 9 A particularly unique stable alternating-twist yarn is prepared using the procedure of Example 1 with the jet of FIGURES 45 by supplying air alternately to one fluid conduit and then the other but also providing for overlapping of these air supplies so that air is successively supplied first to one fluid conduit, then to both conduits, then to the other conduit, then to both conduits, and so on. The product is an alternating-twist yarn in which the twisted bundle segments are separated by segments having zero bundle twist and in which the filaments are interlaced into a unitary coherent strand segment, the filaments being individually twisted within the bundle.

Numerous process modifications or variations are pos sible within the framework of the foregoing examples. For instance, by employing continuous upstream heating or other forms of plasticizing with the intermittent processes of Example 1 or 2, the average twist level in the yarn can be considerably increased with additional setting attendant with the subsequent cooling of or removal of plasticizer from the twisted yarn. With the continuous downstream application of size during intermittent twisting, the alternating-twist is set; with continuous upstream size application, yarns having random length segments of exceptionally high level of twist are obtained. Many novelty eitects can be achieved by twisting plied yarns or staple yarns prepared from materials dyed different colors. A large number of useful products, all based on alternating-twist, are prepared using multiple twisting techniques, whereby several twisters are disposed in one of two principal arrangements:

(1) The pyramidal array, wherein two or more yarns are separately twisted, then combined, and the resulting structure(s) twisted, etc.

(2) The tandem array, wherein two or more twisters are arranged in series, the separate yarns being introduced into the bundle in a stepwise fashion, one at each twister. Numerous variations or permutations of these basic arrangements are possible. In any such arrangement, the later-encountered twisters should have larger yarn passageways in order to accommodate the progressively increased bulk or diameter of the yarn bundle. The individual twisters are preferably operated out of phase with respect to one another. The various products exhibit braided or cable-like structures which are very stable to tension because of their plied and balanced character. By varying the twisting frequencies, the direction of twisting, and the tension in the yarn, a wide variety of alternating twist braided yarns can be produced.

Alternating-twist yarns are useful in the place of conventional twisted yarn in numerous applications, primarily in warp and/or filling uses, or in tricot knitting. Yarns prepared at average twist levels of from about 1 to about 5 t.p.i. and at period lengths of from about 18 to inches may be used to prepare plain weave, satin or tafifeta fabrics substantially equivalent to the comparable fabrics prepared from ordinary twisted yarns. Numerous novelty fabrics can be prepared from alternating-twist yarns of high (greater than about 5 t.p.i.) average twist level, taking advantage of the controlled variation in luster and cross section characteristic of these yarns, Exceptionally high levels of alternating-twist are achieved by twisting the yarn, in a warp, during weaving. Mechanical means are employed to clamp the twist at reversal points, permitting yarn having upwards to 50 or more average t.p.i. and extremely acute reversals.

The process of this invention is of exceptional value in improving the handling characteristics of zero-twist yarn. By zero-twist yarn is meant yarn having no substantial true twist, excluding the omnipresent slight twist in the yarn resulting from normal handling, e.g., twist resulting when removing yarn from a stationary package or due to traversing the yarn, or the twist which results from passing the yarn over skewed or rotating guides, all of which, from a practical standpoint, are negligible. Quills prepared from alternating-twist yarns exhibit improved take-0. T characteristics as compared with known zero-twist yarn, and yarn tensions remain practically constant throughout the take-oi? cycle. Beams prepared from alternatingtwist yarn, twisted in the Warp, can be backwround without the formation of filament ringers, and with or without the retention of twist, the latter case permitting for the first time the backwinding of a warp of zero-twist yarn without resort to slashing or ordinary process twisting. Yarn having about 1 average t.p.i. or" stable alternating-twist exhibits at least a 10% reduction in the coefiicient of friction, reducing wear against guides, pins, and the like, and permitting a corresponding improvement in yarn mechanical quality. The process of this invention, when employed during the drawing operation, results in improved yarn quality since broken filaments and the like are twisted back into the yarn bundie, eliminating subsequent wraps, stripbacks, etc. The instant process also serves, generally, to compact the yarn bundle, facilitating many of the conventional textile operations which follow. Many novelty yarns are produced by plying and blending yarns or staple fibers in accordance with this invention, particularly if the blend consists of material dyed different shades or colors. Similar novelty effects are obtained by applying alternating-twist to side-by-side monofilaments. In a manner similar to that whereby packaging characteristics are improved, the process of this invention permits multiple-end operations on yarn previously given an alternating-twist then converged into a tow, e.g., drawing, dyeing, washing, etc., since the tow may be subsequently broken down to the original yarn bundles, owing to the alternating-twist which maintains the yarn identity while it is in the tow. Such a tow-splitting process permits numerous operations on continuous filament yarn which would be otherwise highly impractical. According to this invention at least 0.5 t.p.i. average twist and preferably at least 1 t.p.i. of alternating-twist is required to obtain the indicated improvements in zerotwist yarn handling characteristics; lower levels of twist result only in marginal benefit at best. Twist period lengths of about 16 feet or more are suitable. Note, however, that at a given level of twist, a decrease in twist period results in a corresponding reduction in the length of the twist eversal sections, hence the shorter twist periods are generally preferable.

The production of yarns of intermediate alternatingtwist level (0.55.0= average t.p.i.) has been exemplified. levels of alternating-twist (greater than about 5 average t.p.i.) are produced similarly, and very high levels (about 20 average t.p.i. or more) are produced by intermittent size or adhesive application, which is accomplished utilizing me apparatus of FIGURE 9, employing therewith a reciprocating guide at. 31, application roll 32, and eyelet guide 3 5, whereby yarn 14 alternately contacts applicator roll 32 (yarn position 14 then is Without contact therewith (yarn position Ma). The heating means 33 may also be used, as described earlier, to facilitate drying of the size or adhesive. In this method, superimposed secondary variations of wist are imposed on the product due to the tension change in the yarn at position 14 versus position 14a. This effect also occurs with a traversing windup, and is used to advantage with the fluid twist of FIGURE 6. When such secondary variations of twist are to be avoided, idler roll 17 of FIGURES 7 and 8, which tends to damp such varying tensions, is used; conversely, to further this effect, that roll is usually omitted. In extending these principles, the process of this invention can be used with conventional twisted yarn to produce a product with stable alternating-twist, the net sum of which is greater than zero. Such products are produced thereby having uniformity greatly improved over the known prior art procedures discussed hereinabove.

In addition to those described earlier, yarns useful in this process include those having a, cruciform, or otherwise modified cross sections, since such yarns twist at a high rate due to their irregular surface and increased surface area. This process is quite useful with elastomcric yarns because of the very low operating tensions permitted during twisting. Yarn to be twisted may contain any or" the usual textile additives, e.g., dclusterants, antioxidants, etc., and may be finished in accordance with accepted practice. Although a quite wide range of yarn denier and filament count may be used, e.g., from monofilainents to a tow, when extremely lar e or small yarn bundles are twisted, twister dimensions should be adjusted according to the foregoing discussion.

Use of the pneumatic twister in the process of this invention is of considerable advantage. Such an apparatus is inexpensive, requires little maintenance due to the absence of moving or rotating parts and minimum yarn contact (no yarn degradation), is practically instantaneous in its action, e.g., when changing direction of twisting or during intermittent twisting, and is very economical to operate. Moreover, such twisters are readily adaptable to operate on extremely close centers, as required in warp twisting. When the twister conforms to the operable and/ or preferred dimensions as indicated hercinabove, uniform and reproducible twisting is obtained.

The process of this invention permits yarn production at exceedingly high twisting rates at exceedingly high throughput speeds over wide ranges of tension, including the very lowes The susceptibility of the process to variations in yarn tension, speed, etc., during twisting permits a number of useful process departures from the more important embodiments of intermittent twisting, including production of alternating-twist yarns by the controlled variation of such factors during continuous unidirectional twisting. The process may be employed at most stages of textile operations, such as during beaming, spinning, drawing, weaving, and the like. The various alternating-twist products, which exhibit a surprising degree of utility and twist retentivity, may be used in the place of conventional twisted yarn in numerous applications, resulting in considerable saving and increased production achieved with improved yarn quality, or to improve the handling or characteristic of zero-twist yarn, with comparable benefit. Other advantages inherent in the practice of this invention will occur to those undertaking its practice.

The claimed invention:

1. A process for producing a stable alternating twist single bundle yarn continuously from filamentary strand structures composed of a plurality of textile filaments, comprising false-twisting a continuously-fed multifilament strand and varying the rate of twisting so that the twist in-' ermittently accumulates and passes downstream with the strand, said twisting being carried out by directing a jet of fluid against successive segments of the multifilament strand to momentarily separate the filaments and simultaneously twist the strand for an intermittent duration of twisting adjusted to less than the time required to establish equilibrium twisting conditions, with the strand under a tension sufficient to prevent twist doubling and less th tensions which will remove the alternating twist impa to the yarn, to introduce an average twist level of at least 0.5 turn per inch in the yarn.

2. The process of claim 1 in which the rate of twisting is varied by intermittently changing the rate of ilow of twisting fluid.

3. The process of claim 1 in which the rate of twisting is varied by intermittently changing the direction of flow of twisting fluid.

4. The process of claim 1 in which the rate of twisting is varied by intermittent application of size upstream of the twister.

5. The process of claim 1 in which the rate of twisting is varied by intermittently varying the yarn tension.

6. The process of claim 1 in which the rate of twistingis varied by intermittently varying the yarn speed.

21 22 7. The process of claim 1 in which the strand is a con- 2,100,588 Claus Nov. 30, 1937 tinuous filament yarn. 2,515,299 Foster et al. July 18, 1950 8. The process of claim 1 in which the strand is a staple FOREIGN PATENTS am. y 355,447 Great Britain Aug. 27, 1931 References Cited in the file of this patent UNITED STATES PATENTS 984,195 Cooper Feb. 14, 1911 

1. A PROCESS FOR PRODUCING A STABLE ALTERNATING TWIST SINGLE BUNDLE YARN CONTINUOUSLY FROM FILAMENTARY STRAND STRUCTURES COMPOSED OF A PLURALITY OF TEXTILE FILAMENTS, COMPRISING FALSE-TWISTING A CONTINUOUSLY-FED MULTIFILAMENT STRAND AND VARYING THE RATE OF TWISTING SO THAT THE TWIST INTERMITTENTLY ACCUMULATES AND PASSES DOWNSTREAM WITH THE STRAND, SAID TWISTING BEING CARRIED OUT BY DIRECTING A JET OF FLUID AGAINST SUCCESSIVE SEGMENTS OF THE MULTIFILAMENT STRAND OF MOMENTARILY SEPARATE THE FILAMENTS AND SIMULTANEOUSLY TWIST THE STRAND FOR AN INTERMITTEN DURATION OF TWISTING ADJUSTED TO LESS THAN THE TIME REQUIRED TO ESTABLISH EQUILIBRIUM TWISTING CONDITIONS, WITH THE STRAND UNDER A TENSION SUFFICIENT TO PREVENT TWIST DOUBLING AND LESS THAN TENSIONS WHICH WILL REMOVE THE ALTERNATING TWIST IMPARTED TO THE YARN, TO INTRODUCE AN AVERAGE TWIST LEVEL OF AT LEAST 0.5 TURN PER INCH IN THE YARN. 